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Starter Circuit Question

Definitely too much voltage drop. I agree with @kmead that high resistance at the terminals is very common. And I also do as he suggested by replacing them with ring terminals. That kills several faults; new connectors have no corrosion, rings are a 'bolted' tight connection vs a 'push-on' loose connection, the wire gets trimmed back to fresh material when the rings are installed, and rings typically have a larger contact surface than push-on's.

However the terminals are not the only place corrosion can cause high resistance. In the two complete X1/9 wire harnesses that I've fully dissected I found several spots along the wire where corrosion existed internally - along the wire core inside the insulation. Externally the insulation appeared good, no signs of damage, and no other visual indication that there was an internal problem. But the resistance was high even after excluding the terminals. So I began stripping off the insulation and discovered the bad wire(s). Obviously the suspect quality wire was contaminated when manufactured, allowing it to corrode despite the insulating jacket. In these cases replacing the entire length of the leads solved the problem.

This sort of internal corrosion can also exist in the battery cables. Especially with the incredibly long ones, the under-sized charge (alternator) wire, and the grounding straps. Not to mention the notorious "brown" wires. Good places for some upgrades all around. ;)

In addition to upgrading the wires, cables, connectors/terminals, etc, I also add relays to all of the high-load circuits...as has been suggested several times above. :) I guess we're saying the X's electrical system as a whole is another general problem area that needs a complete overhaul.
 
I’ve had a few electrical problems with the car and measured significant voltage drops from battery to loads. In many cases cleaning fuses and other connections made a significant difference. As an example, this greatly improved the operation of the electric windows. I have added a relay to the ignition system in response to a voltage drop at the coil, but it wasn’t the root cause of a stalling problem. It turned out to be the AFM. More work is needed. I’ll keep posting as I work through the issues.
 
I am going to add a relay to the starter solenoid circuit. Should I be putting a reverse biased catch diode on the terminals? Since the solenoid is essentially an inductor, when the solenoid is shut off the collapsing field would create a voltage spike across the relay terminals which would cause arcing as the contacts open. Unfortunately, I don’t have the equipment to check this. Any thoughts?
 
beezee said:
I am going to add a relay to the starter solenoid circuit. Should I be putting a reverse biased catch diode on the terminals? Since the solenoid is essentially an inductor, when the solenoid is shut off the collapsing field would create a voltage spike across the relay terminals which would cause arcing as the contacts open. Unfortunately, I don’t have the equipment to check this. Any thoughts?
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You can buy a relay with diode internal to it (they also make the with resisters fyi). Good idea.
 
kmead said:
You can buy a relay with diode internal to it (they also make the with resisters fyi). Good idea.
Click to expand...
Internal diodes are on the coil side. I am considering putting one across the contacts. It could increase the contact life, but if the diode fails….

Maybe I am overthinking this.
 
beezee said:
Internal diodes are on the coil side. I am considering putting one across the contacts. It could increase the contact life, but if the diode fails….

Maybe I am overthinking this.
Click to expand...
I would not add the diode. TE has an app-note about relays where they say that too low a current (contact side, not coil side) reduces the cycle life of the relay, as the lack of arcing allows gunk (scientific term) to build up on the contacts.

I have a starter relay installed, and at $5 for a brand name relay, I'll just replace it if it wears out.
 
beezee said:
Internal diodes are on the coil side. I am considering putting one across the contacts. It could increase the contact life, but if the diode fails….

Maybe I am overthinking this.
Click to expand...
Diodes are going to do squat nothing. The device operating/powering on the relay is a switch not a semiconductor which can be sensitive to inductive high voltage spikes kicking back into that semiconductor device. Adding a diode across the relay coil is the typical and common way to protect a semiconductor device driving a relay coil, does not apply to a relay coil driven by a switch.

Diode across the relay contacts could cause untented current flow depending on the orientation of the diode. In this specific example if the diode is wired in with anode towards positive, cathode towards negative (diode forward biased) there will be current flow regardless of the relay contact position. The diode must be installed/wired with cathode towards positive, anode towards negative (reverse biased) for adding a diode wired across the contacts to even work.. With all that the diode will do about zilch to protect or reduce relay contact wear..

Relays are not created equal, the most common automotive relays today are el-cheap-O clones of the power relay invented by Bosch decades ago. These cheap-O power relays should not be trusted or relied upon for anything that needs to work in a moto electrical system. Sure one can justify the cheap-O relay by rationalizing .. "Oh, will just replace the relay if / when it fails"... except when you're out in the middle of no-where with no possible means to fix it...

This is the hidden and often not appreciated aspect of proven reliable/durable electrical bits like relays..

Consider using a vintage genuine Bosch power relay salvaged from one of the Fiat parts cars.. as these are a proven durable/reliable design. If the Bosch power relay is in good condition, it will continue to serve and function good for a while..

Alternatives would be power relays offered by Bosch..

Speedway motors:
www.speedwaymotors.com

Speedway Single 70 Amp Relay Module

www.speedwaymotors.com www.speedwaymotors.com

also sold by Leash electronics:
www.leashelectronics.com

1HO Single 70amp Relay Module

Single 70 amp relay module. Has heavy duty 70 amp industrial relay. Uses heavy duty J-case/FMX fuses (NOT INCLUDED).Can be wired for positive or ground triggered.Fuses available in FMX/J case fuse category#10 battery input and relay output studs. Led indictor on output. ALL OUR RELAYS ARE...
www.leashelectronics.com www.leashelectronics.com

Marine power relays like those offered by Bluewater are another possible choice:

All goes back to the discussion about the 500amp EV contactor, post# 7
Rupunzell

Post in thread 'Beginning to deal with the electrical system in# 209...'

beezee said:
Why the 1000V contactor? Is it just something you had available?
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Not the 1000 volt rating that is significant for the electrical system in# 209, it is the 500 amp contact rating that is significant.
Has a mechanical cycle rating of 1,000,000 cycles, cycle rating of 10,000 switching 200 amps. When used in a vintage moto application these EV contactors should last/work ok.
TE series EV200 contactor-1.jpg


TE series EV200 contactor-2.jpg


This contactor will be used for main power much like a FIA regulation kill switch which is manually operated. The EV contactor allows operation by very small switch..

Beyond the EV...
  • Like


Bernice
 
Thanks for the reply. A 150A relay would be major overkill in a circuit that measures 22A. I looked at the Speedway and Leash options. Both of these use a PCB mount 70A Panasonic relay which can be found elsewhere for around $5. The benefit of these options is they offer ring lug terminations. I have been looking at 40A relays with a mounting tab that can be easily mounted under the dash. Once I finalize my solution I will post it.

Interestingly, I have never experienced a relay failure in any car I have owned but I once owned a Ford Escort that burned up a headlight switch. My wife’s Fiat 500 has burned up its headlight wiring, smoked the alternator, lost power to the cigarette lighter (I replaced the fuse to no avail) and suffered a failure of the trunk switch due to corrosion. Alessandro Volta got Italy off on the right track, but they seem to have struggled with electricity since.
 
beezee said:
Thanks for the reply. A 150A relay would be major overkill in a circuit that measures 22A. I looked at the Speedway and Leash options. Both of these use a PCB mount 70A Panasonic relay which can be found elsewhere for around $5. The benefit of these options is they offer ring lug terminations. I have been looking at 40A relays with a mounting tab that can be easily mounted under the dash. Once I finalize my solution I will post it.

Interestingly, I have never experienced a relay failure in any car I have owned but I once owned a Ford Escort that burned up a headlight switch. My wife’s Fiat 500 has burned up its headlight wiring, smoked the alternator, lost power to the cigarette lighter (I replaced the fuse to no avail) and suffered a failure of the trunk switch due to corrosion. Alessandro Volta got Italy off on the right track, but they seem to have struggled with electricity since.
Click to expand...
Even the 70A relay is overkill. A regular 40 A Panasonic automotive relay is rated for 100,000 cycles at 40 A. Heavy PCB mounted relays are a problem on their own; solder has poor mechanical properties, and a heavy relay in a vibration environment often cracks the solder joints. BMW experienced this with their LKM module a number of years back, and I have personally seen this type of failure several times.

You may find that the spare tire well is a better place for a starter relay than under the dash. You have a very solid 12V supply at the starter lug, and the starter trigger terminal and trigger wire are close by. This is my setup; starter relay being the middle one:

index.php
 
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ng_randolph said:
Even the 70A relay is overkill. A regular 40 A Panasonic automotive relay is rated for 100,000 cycles at 40 A. Heavy PCB mounted relays are a problem on their own; solder has poor mechanical properties, and a heavy relay in a vibration environment often cracks the solder joints. BMW experienced this with their LKM module a number of years back, and I have personally seen this type of failure several times.

You may find that the spare tire well is a better place for a starter relay than under the dash. You gave a very solid 12V supply at the starter lug, and the starter trigger terminal and trigger wire are close by. This is my setup; starter relay being the middle one:

index.php
Click to expand...
Thanks, that setup is very similar to what I am currently considering. I am looking for a suitable mini iso relay socket and proper crimp terminals which is time consuming given all the variations that are available.
 
If you wish to avoid a relay that uses "push-on" spade terminals for the main power leads, preferring one with "ring" terminals, but also don't want to utilize the PCB mounted type, you can find standard style contact relays with stud-posts for ring terminal attachment. They tend to be higher amp ratings than you really need, but they offer the combination of features you are seeking. And the size isn't much different from any standard 12V automotive relay. Here's a random pic as an example:
GR19_C.png
 
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